1. Technical Field
This invention relates to a printing press, and more particularly, a color printing press having a plate cylinder with four plate image segments, an impression cylinder with five impression segments, and a blanket cylinder with four blanket segments cooperating with the plate and impression cylinders for transferring offset images onto a print media.
2. Prior Art
Rotary offset printing machines incorporating prepress operations and printing operations into one printing press have been used for a number of years. The basic mechanisms, principles, and steps of operation for modern rotary printers can include image-exposure methods, image-ablation methods, computer-to-plate printing methods and other conventional printing methods known in the art. In computer-to-plate printing methods, an image is formed on an image plate by a laser exposure method, or the like, thereby performing the prepress image process with digital data. Such digital images may then be transferred onto printable media using conventional techniques, and magnetically charged ink-based systems, for example.
In conventional multi-color printing presses, the print media may be transferred to one or more impression cylinders, which grip the print media from a transfer gripper and roll the print media against one or more blanket cylinders for printing. Transfer cylinders and associated gears have been used to transfer print media from one impression cylinder to the next or from one blanket cylinder to the next. However, such structures are complex, expensive and introduce some problems.
For example, smearing can result because the printed surface of the transferred print media is directed inward on each transfer cylinder. The printed surface of the print media faces outward toward the blanket cylinder when the next impression cylinder grips it. Therefore, the need for special coatings, multiple transfer gripping mechanisms, special non-stick screens, large precision-built transfer cylinders, and even complex systems for air-cushioning the print media as it is carried around the transfer cylinder have been employed to minimize this smearing problem. As a result, the cost of manufacturing multi-color offset printers with such additional components has been very high.
Further, because of the need to properly adjust registration of the print media as it is received by each impression cylinder, transferred to each transfer cylinder and then received by each subsequent impression cylinder, the time and expense to set up any given multiple color offset printing job has been substantial. As a result, multiple color offset rotary printing has not been economically feasible for most small printing jobs requiring less than several thousand copies.
In summary, prior art prepress and printing machines require complex components and excessive floor space. The need for using several imaging heads, blanket cylinders, plate cylinders, and/or impression cylinders increases costs. Therefore, there is a need to provide a prepress and printing machine with fewer components to reduce the size thereof, associated costs and the efficiencies thereof.